The world is the world because it's the world. Makes perfect sense. Except, there are many different ways to experience the world. So, why do you experience it the way you do? Well, without going down the rabbit hole too far, there is a simple concept that can really narrow down the infinite number of influences and variables.
A big part of what explains life, and most likely the biggest part, is that how we experience our parents is how we end up experience the world. If parents are understanding and forgiving, then it feels like the world will generally give you the benefit of the doubt. If parents are more on the negligent side then it feels like you're pretty much on your own and there's not much support out there. If parents are cruel then it can feel like the world is just one big terrible slog.
It may sound like an oversimplification, but after having spent years teaching little kids, it was amazing to see the variety of assumptions and expectations the kids came to school with. Additionally, actually identifying the specific influence is surprisingly difficult.
Part of the complication is that each person also plays a role in how they interact with their personal world. That's where siblings come in. Research has been discovering that siblings have a huge impact on a person's identity. Each child is looking to fill a unique role, and rightfully so - it's the easiest way to feel valued. The first child might be a leader, so the second decides to be an artist, and the third sees an opening in the care-taking realm.
Generally, there is a great deal of overlap between siblings, but our brains are naturally drawn to the differences - it's a great way to create diversity in skills. On the other hand, this can easily lead to a number of other issues...but I'll get into that a different time.
There are a few ways to react to this viewpoint. It might be, "Well of course, what else would define a small child's world?" Or maybe there's some anxiety around how arbitrarily "the world" can be shaped. I personally take comfort in it, because it means that I can change the way I experience the world. If something's not working, I can just go make another world. As much as a child is pretty much at the mercy of home life, an adult can mix things up, try things out, and tweak things until negative feelings are replaced by a healthier sense of well-being.